Method for making tuning fork resonator

ABSTRACT

There is disclosed a tuning fork resonator with materials of high relative magnetic permeability joined by forcibly causing one of the materials to penetrate the other without the use of heat or filler material. The joined materials form part of a magnetic flux path therebetween. Penetration of a first of the materials into the second results in a displacing of material, the flow of which is restricted to form a projection of predetermined size and shape.

United States Patent [191 Vollet METHOD FOR MAKING TUNING FORK RESONATOR [75] Inventor: George L. Vollet, Massapequa, NY.

[73] Assignee: Philamon Laboratories, Inc.,

Westbury, NY.

22 Filed: Mar. 18, 1971 21 App]. No.: 125,624

' Related U.S. Application Data [62] Division of Ser. No. 766,278, Oct. 9, 1968,

abandoned.

[52] U.S. Cl 29/169.5, 29/432.1, 29/505, 29/511, 84/409 [51] Int. Cl B29d 17/00 [58] Field-of Search 29/169 .5, 607, 432.1,

[56] References Cited UNITED STATES PATENTS 2,095,885 10/1937 Moreira et al. 29/432 X 2,537,723 1/1951 Ward 179/115.5

[ Oct. 16, 1973 Strain et a1. 29/432 2,959,746 11/1960 Sears 331/116 3,083,607 4/ 1963 Reifel 84/409 3,130,489 4/1964 Schlage.. 29/432 3,191,268 6/1965 Matea 29/511 X 3,477,115 11/1969 Martin et a1...... 29/47l.1 X 3,481,140 12/1969 Tuetey 29/177 X 3,571,903 3/1971 Persson 29/432.l 3,680,195 8/1972 Lejdegard 29/432.1

Primary Examiner-Charles W. Lanham Assistant Examiner-Victor Al DiPalma Attorney-Darby & Darby [57] ABSTRACT 7 Claims, 6 Drawing Figures Patented Oct 16, 1973 FIG.

FIG. 3

4 INVENTOR GEORGE L. VOLLET ATTORNEYS METHOD FOR MAKING TUNING FORK RESONATOR This is a division of Application Ser. No. 766,278 filed Oct. 9, 1968 now abandoned.

This invention relates to tuning fork resonators and more particularly to a method and apparatus for joining magnetizable parts of such resonators.

Tuning fork resonators of the type disclosed in US. Pat. No. 2,732,748, for example, include a tuning fork which vibrates between magnets affixed to a base member which, in turn, is made of a material of high relative magnetic permeability. A magnetic flux path between the tuning fork, the magnets and portions of the base member is characteristic of such resonators.

In fabricating tuning fork resonators, it is commonplace to solder the permanent magnets to upstanding leg portions of the base member. The result is a relatively weak bond between the magnet and base, and a high reluctance or resistance to magnetic flux. Welding of the magnets to the base legs disturbs the magnetic and physical properties of the materials being joined and distorts the shape of the final assembly dueto the heat often required.

It is an object of the present invention to provide a tuning fork resonator which includes both permanent magnets and a stuning fork each supported by a base member, wherein the magnets are secured to the base member by forcibly causing each to partially penetrate the base material and be permanently held thereby.

Another object of this invention is to provide a method and apparatus for making the above tuning fork resonators, which enables a relatively inexpensive and less time-consuming manufacture of these articles.

A still further object is to provide a method of joining materials of different hardness without the use of filler material or heat.

Yet another object is to provide a tuning fork resona tor with superior reluctance properties along its magnetic flux paths.

The present invention fulfills the aforementioned objects and overcomes limitations and disadvantages of prior art solutions to problems affecting the manufacture of tuning fork resonators. According to one aspect of the invention, a tuning fork resonator includes a channel-shaped base member having upstanding legs extending from a floor portion, the base member preferably being formed from a material of high relative magnetic permeability. A cylindrical permanent magnet which is to be joined to the base member is supported in and extends from a bore defined by a support member which, in turn, is supported on the bed of a hydraulic press. A ram member, formed with a cylindrical bore of a diameter smaller than that of the magnet is secured to the ram of the hydraulic press such that the respective bores are coaxial. A first leg of the base member is positioned over the projected axis of the magnet between the magnet and the ram member, whereupon the press is actuated. The ram member drops, striking the first leg, and forcibly causes the magnet to penetrate the first leg a predetermined distance, for example one-half the thickness of the leg, thereby displacing first leg material into the ram member bore and forming a cylindrical projection. Material of the base member first leg immediately adjoining the magnet permanently holds the latter in place, also providing a potential magnetic flux path therebetween of relatively low reluctance.

This invention will be more clearly understood from the following description of a specific embodiment of the invention, together with the accompanying drawing, wherein similar reference characters denote similar elements throughout the several views, and i which: I

FIG. 1 is a fragmentary perspective view of a tuning fork resonator according to the present invention;

FIG. 2 is a fragmentary sectional elevational view of joining apparatus according to the invention;

FIG. 3 is a fragmentary sectional elevational view looking along the line 3-3 of FIG. 2;

FIG. 4 is an enlarged fragmentary sectional elevational view of a magnet shown in FIG. 3;

FIG. 5 is a fragmentary sectional elevational view of a staking operation according to this invention;

FIG. 6 is an enlarged sectional elevational view of the magnet and staking apparatus shown in FIG. 5.

Referring now in more detail to the drawing, FIG. 1 shows an electrically responsive tuning fork resonator 10 which includes a channel-shaped base member 11 formed with two upstanding legs 12 and 13 each extending from a floor portion 14. Magnetizableobjeets or permanent magnets 15, 16, 17 and 18 are each supported by one of the legs in a manner described below, each magnet being formed from a material of high relative magnetic permeability, such as aluminum-nickelcobalt alloys Alnico l or Alnico 8. Magnets 15-18 are preferably cylindrical in shape but may be formed in any desirable shape, such as with square, rectangular or any polygonal cross section. A tuning fork 19 is shown in phantom in FIG. 1 secured on step portion 20 of base member 11 and extending between magnets 15 and I6, and 17 and 18, respectively. Tuning fork 19, when excited, vibrates between the magnets in legs 12 and 13.

Permanent magnets 15, 16, 17 and 18 may be magnetized either prior to or after their attachment to the legs of base member 11. The base member material is of high relative magnetic permeability, preferably Carpenter high permeability 49 or similar type steel alloy, formed from an annealed cold rolled sheet strip. In the embodiment of the tuning fork resonator shown in FIG. 1, the relative hardness of each of the magnets is greater than that of the base member. Magnets 15, 16, 17 and 18 are preferably of Rockwell hardness C-45 and C-56, when made from Alnico l and 8, respectively. Base member 11 is preferably of Rockwell Hardness B-65, when made from Carpenter high permeability 49 alloy. In stating that magnets 15-18 are harder than base member 11, it is understood that said magnets not only possess a greater resistance to local penetration, yielding and scratching, but also include favorable composite penetration properties, including but not limited to yield strength, .work hardening, true tensile strength, modulus of elasticity and'ductility.

Describing now the method and apparatus for joining the magnets with the base member legs, a support member generally designated numeral 21 is mounted upon the upper face 22 of a bed 23 of a conventional hydraulic-type press. Support member 21 includes an upper plate 24 secured to a lower plate 25. Upper plate 24 is formed with cylindrical bores 26 and 39 which extend from an upper face 27 of plate 24. Plate 24 is further formed with recesses 28 and 38 extending into plate 24 from side surface 29 and bottom surface 30 thereof. .Lower plate 25 is formed with cutout 31 which, when assembled in the position shown in FIG.

2, underlies recesses 28 and 38. Plates 24 and 25 are joined by bolting or other suitable fastening means.

A ram plate 32 is shown in FIG. 2 secured, such as by bolting, to a portion of a hydraulic press ram 33. Ram plate 32 is formed with cylindrical bores 34 and 36 extending coaxially with respect to bores 26 and 34 between surfaces 35 and 36 of the plate. Bores 34 and 37 are each of a diameter smaller than the diameter of magnets -18.

In operation, assuming for purposes of illustration that magnets 17 and 18 are already secured to leg 13 of base member 11 and that magnets 15 and 16 are to be joined with leg 12, magnets 15 and 16 are positioned within bores 26 and 39 such that ends 40 and 41 thereof project out of these bores above upper face 27 a predetermined distance which is a function of the material thickness of leg 12. Base plate 11 is thereafter positioned such that the inside portions of leg 12 rest upon ends 40 and 41 of magnets 15 and 16. In this position, leg 13 with magnets 17 and 18 secured thereto extends into cutout 31. The press operator actuates the press in a conventional manner, causing ram 33 and ram plate 32 to drop against leg 12. Further movement of ram plate 32 toward upper face 37 results in material of leg 12 in contact with ends 40 and 41 yielding, thereby permitting penetration of magnets 15 and 16 into this leg, and simultaneously causing a displacement of leg material into bores 34 and 37 (FIG. 3). The depth of penetration of each magnet into a base member leg is preferably approximately one half the thickness of the respective leg. This displaced material takes the shape of cylindrical plugs or projections each of a diameter smaller than that of the magnet associated with each. Projections 42, 43, 44 and 45 are each associated with magnets 15, 16, 17 and 18, respectively, and provide a portion of a magnetic flux path between the magnets and the base legs. Projections 42-45 further structurally reinforce the leg material adjoining the magnets after their joining with the base member and provide a source of elastic potential energy tending to re-enter the space occupied by the respective magnets. The magnitude of this energy is a function of the physical properties of the base leg material. For magnet diameters of 0.128 inches, projections 42-45 are preferably 0.125 inch in diameter.

The edge of magnets 15 and 16 formed by the intersection of ends 40 and 41 thereof and their cylindrical surfaces is preferably slightly rounded with a radius of curvature of varying from about 2 percent to about 25 percent of the depth of penetration of the magnets into the respective base leg. For magnet diameters of 0.128 inches and base leg thicknesses of 0.034 inches, the preferable depth of penetration of the magnet into the leg is 0.017 inches, the magnet edges preferably being rounded 0.001 inch. This rounding of the magnet edge yields more favorable retention properties.

Each of the magnets which has penetrated the base leg is permanently held in place by a combination of effects. Firstly, it is believed that a local coalescence of magnet and base member materials in contact with one another occurs as a result of the force with which each magnet is caused to penetrate each leg. An interaction between adjoining base member and magnet surfaces results in a metallic bond being formed which has a tendencyto permanently retain the respective magnet in place. Secondly, the forcible entry of each magnet into a base member leg causes a partial shearing of leg material as well as the introduction of compressive forces in the penetrated leg, these forces acting in the plane of the leg. Thus, circumferential compressive forces are exerted radially inwardly against the outer surfaces of the magnet, frictionally preventing movement of the magnet with respect to the base member leg to which it is secured. It is within the scope of this invention to secure each of the above magnets 15-18 to a base member leg solely by the friction forces last discussed and without the aid of coalescence between magnet and base member materials. Furthermore, while this theory of coalescence is believed correct, the utility and operability of the present invention is in no way predicated upon the theory.

The walls of upper plate 24 defining bores 26 and 39 serve both as supports and guides for the magnets during their penetration into leg 12, thereby eliminating the possibility of magnet cracking or chipping.

FIG. 3 illustrates the relative position of punch plate 32 at the end of the stroke of ram 33, showing portions of leg 12 adjacent magnets 15 and 16 compressd between face 27 of plate 24 and surface 35 of the ram plate. Of course it is contemplated that the surface contour of plates 32 and 24 be such as to compensate for leg material spring-back.

Removal of base 11 from support member 21 after ram 33 retracts upwardly is accomplished by lifting the workpiece vertically until magnets 15 and 16 are clear of bores 26 and 39. It is during this lifting and removal of the workpiece from the joining apparatus that recesses 28 and 38 serve as clearances for magnets 17 and 18 already secured to base memberleg 13. After removal of this workpiece from support member 21, others may be assembled in rapid succession in much the same manner.

In other embodiments of this invention, not shown, different size magnets may be joined with base member legs in varying depths of penetration. It is also obvious to reverse the position of support member 21 and ram plate 32 such that the former is movable while the latter is stationary, or both members maybe movable.

Magnets 15-18 may be permanently magnetized either before or after being joined with the respective base member leg. In the preferred embodiment shown in FIG: 1, the magnets are magnetized after the joining operation. No filler materials, such as solder or flux, are used in securing magnets 15-18 to the base member, nor is any pre-joining treatment or preparation of the base member legs necessary.

A further optional-staking operation is illustrated in FIGS. 5 and 6, and is performed for purposes of insuring retention of each magnet within its associated base member leg. Staking dies 46 and 47 are shown in FIG. 5 supported in slots 48 and 49 formed in a die support 50. Each of staking dies 46 and 47 includes a relatively sharp annular edge 51 formed by converging surfaces 52 and 53. The diameter of edge 51 is slightly larger than that of the magnets, approximately 0.030 inch larger for magnet diameters of 0.128 inches. A cylindrical cavity 54 is formed in each of dies 46 and 47 to receive portions of magnets 15 and. 16, for example, with approximately 0.0005 inch nominal clearance between the outer surface of the magnets and the die walls defining cavity 54.

Die support is supported on the bed of a hydraulic press and is further formed with slots 55 and 56 for receiving magnets 17 and 18 during the staking of magnets, 15 and 16, to be described below. A ram plate 57 similar to plate 32 is secured to the ram of the press.

The staking operation includes taking a base member 11 with magnets 15-48 already joined with its legs 12.

and 13 and placing the cavities 54 of staking dies 46 and 47 over magnets 15 and 16, for example. The base member and staking dies are then positioned as shown in FIG. 5 with dies 46 and 47 resting in slots 48 and 49, and with magnets 17 and 18 located in clearance slots 55 and 56. The operator of the press thereafter actuates the press, causing punch plate 57 to move toward die support 50 until it engages outer surfaces of base member leg 12 adjacent projections 42 and 43. Further downward movement of punch plate 57 results in annular edge 51 of each of the staking dies 46 and 47 penetrating base leg material adjacent the point of entry of magnets 15 and 16 into leg 12, thereby causing a displacement of leg material in the shape of a ring 58 around and against each magnet. Retraction of punch plate 57 reveals an annular depression around magnets 15 and 16 previously occupied by the displaced leg material. The workpiece may then be removed from the die support and the same procedure repeated for magnets 17 and 18. A preferable depth of penetration of edge 51 into leg 12 is between 0.006 to 0.007 inches for magnet diameters of 0.128 inches and nominal leg thicknesses of 0.034 inches.

The joining of permanent magnets to base member legs and subsequent staking according to the present invention yields an attachment bond or joint three times the maximum strength of conventional soldered joints, at temperatures ranging from -60C to (200C). The presence of projections 42-45, for example, in tuning fork resonator decreases reluctance or resistance to magnetic flow. Of course, it is possible to cause magnets -18 to fully penetrate through legs 12 and 13 by increasing the diameter of bore 34 in ram plate 32 and by increasing the distance which each of the magnets extends from upper face 27, thereby enabling a shearing or punching of each magnet through a base member leg. The distance of full penetration may be equal to the thickness of the base member leg such that magnets 15-18 are finally positioned with one of their ends substantially flush with the outer surface of the respective leg. However, more favorable magnetic flux properties are achieved by partial penetration of each magnet into a leg and this embodiment will be preferred in many situations.

The embodiments of the invention particularly disclosed are presented merely as examples of the invention. Other embodiments, forms and modifications of the invention coming within the proper scope of the appended claimswill of course readily suggest themselves to those skilled in the art.

What is claimed is:

1. A method of joining materials of different hardness, including the steps of: supporting a first object of a first hardness, supporting a second object to be joined with said first object, said second object having a second hardness greater than the first hardness, causing portions of said second object to penetrate portions of the first object, thereby displacing material occupied by said portions of the second object, simultaneously restricting flow of said displaced material to form a projection of predetermined shape extending from a portion of said first object.

2. The method of claim 1, comprising the step of urging material of the first object immediately adjoining said second object against the second object.

3. The method of claim 1, wherein said restricting includes forming said projection such that its greatest transverse dimension is less than the greatest transverse dimension of the second object.

4. The method of claim 1, further comprising the steps of guiding the second object during said penetration.

5. A method of making a tuning fork resonator having a tuning fork supported by a base, comprising the steps of: supporting a first object of high hardness being capable of permanent magnetization, supporting a second object of low relative hardness, said second object being a part of a magnetic flux carrying portion of said tuning fork resonator, and causing portions of said first object to forcibly penetrate portions of the second object, thereby permanently joining said objects.

6. A method of making a tuning fork resonator according to claim 5, further comprising the step of magnetizing said first object.

7. A method of joining materials of different hardness, including the steps of:

supporting a first object of a first hardness, to permit displacement of the material thereof through a predetermined area,

supporting a second object to be joined with said first object substantially at the perimeter of said area said second object having a second hardness greater than said first hardness,

and causing portions of said second object to penetrate portions of the first object along a predetermined axis extending through said area, the maximum depth of said penetration being substantially no greater than the thickness of said first object along said axis, thereby displacing material of said,

first object primarily in a direction along said axis. 

1. A method of joining materials of different hardness, including the steps of: supporting a first object of a first hardness, supporting a second object to be joined with said first object, said second object having a second hardness greater than the first hardness, causing portions of said second object to penetrate portions of the first object, thereby displacing material occupied by said portions of the second object, simultaneously restricting flow of said displaced material to form a projection of predetermined shape extending from a portion of said first object.
 2. The method of claim 1, comprising the step of urging material of the first object immediately adjoining said second object against the second object.
 3. The method of claim 1, wherein said restricting includes forming said projection such that its greatest transverse dimension is less than the greatest transverse dimension of the second object.
 4. The method of claim 1, further comprising the steps of guiding the second object during said penetration.
 5. A method of making a tuning fork resonator having a tuning fork supported by a base, comprising the steps of: supporting a first object of high hardness being capable of permanent magnetization, supporting a second object of low relative hardness, said second object being a part of a magnetic flux carrying portion of said tuning fork resonator, and causing portions of said first object to forcibly penetrate portions of the second object, thereby permanently joining said objects.
 6. A method of making a tuning fork resonator according to claim 5, further comprising the step of magnetizing said first object.
 7. A method of joIning materials of different hardness, including the steps of: supporting a first object of a first hardness, to permit displacement of the material thereof through a predetermined area, supporting a second object to be joined with said first object substantially at the perimeter of said area said second object having a second hardness greater than said first hardness, and causing portions of said second object to penetrate portions of the first object along a predetermined axis extending through said area, the maximum depth of said penetration being substantially no greater than the thickness of said first object along said axis, thereby displacing material of said, first object primarily in a direction along said axis. 